CN114008827B - Current collector for power storage device electrode, method for producing the same, and power storage device - Google Patents

Abstract

The present invention provides a collector for an electrode of an electric storage device, which can realize high output, can maintain high energy density and has excellent output characteristics, a method for manufacturing the collector for the electrode of the electric storage device, and an electric storage device having the collector for the electrode of the electric storage device. The power storage device of the present invention is a power storage device electrode collector comprising an aluminum material and an amorphous carbon film formed on the aluminum material. In the amorphous carbon film, sp ² Bonding carbon and sp ² Bonding carbon and sp ³ Ratio of total amount of bonded carbon (sp ² /(sp ³ +sp ² ) 0.35 or more. In addition, the ratio (sp ² /(sp ³ +sp ² ) Is the ratio measured by the X-ray absorbing fine structure (XAFS) method.

Description

Current collector for power storage device electrode, method for producing the same, and power storage device

Technical Field

The present invention relates to a current collector for an electrode of an electric storage device, a method for producing the current collector for an electrode of an electric storage device, and an electric storage device using the current collector for an electrode of an electric storage device.

The present invention claims priority based on Tokugan Application No. 2019-113900 filed in Japan on June 19, 2019, the contents of which are incorporated herein by reference.

Background technique

In the past, electric double-layer capacitors (see Patent Document 1, for example) and secondary batteries were known as technologies for storing electrical energy. The life, safety, and output density of electric double-layer capacitors (EDLCs) are significantly better than those of secondary batteries. However, electric double-layer capacitors have a problem of having a lower energy density (volume energy density) than secondary batteries.

Here, the energy (E) stored in the electric double layer capacitor is expressed as E=1/2×C×V ² using the capacitance (C) of the capacitor and the applied voltage (V). The energy is proportional to the capacitance and the square of the applied voltage. Therefore, in order to improve the energy density of the electric double layer capacitor, a technology for increasing the capacitance and applied voltage of the electric double layer capacitor has been proposed.

As a technology for increasing the capacitance of an electric double layer capacitor, there is known a technology for increasing the specific surface area of activated carbon constituting an electrode of the electric double layer capacitor. Currently, the specific surface area of known activated carbon is ^1000m2 /g to ^2500m2 /g. For an electric double layer capacitor using such activated carbon as an electrode, an organic electrolyte obtained by dissolving a quaternary ammonium salt in an organic solvent, an aqueous electrolyte such as sulfuric acid, etc. are used as an electrolyte.

Since the organic electrolyte can be used in a wide voltage range, the applied voltage can be increased, and the energy density can be increased.

As a capacitor that utilizes the principle of a double-layer capacitor to increase the applied voltage, a lithium-ion capacitor is known. The negative electrode of a lithium-ion capacitor uses graphite or carbon that can bind or debind lithium ions, and the positive electrode uses activated carbon that can absorb and desorb electrolyte ions, which is the same as the electrode material of a double-layer capacitor. In addition, a capacitor in which either the positive or negative electrode uses activated carbon that is the same as the electrode material of a double-layer capacitor, and the other electrode uses a metal oxide or a conductive polymer as an electrode that produces a Faraday reaction is called a hybrid capacitor. For a lithium-ion capacitor, among the electrodes constituting the double-layer capacitor, the negative electrode is composed of graphite, hard carbon, soft carbon, etc., which is a negative electrode material of a lithium-ion secondary battery, and is an electrode in which lithium ions are inserted into the graphite, hard carbon, or soft carbon. Lithium-ion capacitors have the characteristic that the applied voltage becomes larger than that of a conventional double-layer capacitor, that is, a capacitor in which both electrodes are composed of activated carbon.

However, when graphite is used for electrodes, there is a problem that propylene carbonate, which is known as a solvent for electrolyte, cannot be used. This is because when graphite is used for electrodes, propylene carbonate is electrolyzed, and the decomposition products of propylene carbonate adhere to the surface of graphite, reducing the reversibility of lithium ions. Propylene carbonate is a solvent that can work even at low temperatures. When propylene carbonate is applied to an electric double layer capacitor, the electric double layer capacitor can work even at -40°C. Therefore, in lithium ion capacitors, hard carbon and soft carbon, which are difficult for propylene carbonate to decompose, are used as electrode materials. However, compared with graphite, hard carbon and soft carbon have lower capacity per unit volume of the electrode, and the voltage is also lower (high potential) compared to graphite. Therefore, there are problems such as lower energy density of lithium ion capacitors.

As a new concept capacitor, a capacitor that uses graphite as a positive electrode active material instead of activated carbon and utilizes the reaction of insertion and separation of electrolyte ions relative to the interlayer of graphite has been developed (for example, refer to patent document 2). The following content is recorded in patent document 2. For the previous double-layer capacitor using activated carbon as the positive electrode active material, if a voltage exceeding 2.5V is applied to the positive electrode, the electrolyte decomposition occurs and gas is generated. In contrast, for the new concept capacitor using graphite as the positive electrode active material, even a charging voltage of 3.5V will not cause the decomposition of the electrolyte, and it can work at a higher voltage than the previous double-layer capacitor using activated carbon as the positive electrode active material. If this technology is adopted, the energy density can be increased by about 2 to 3 times compared with the previous double-layer capacitor. Regarding the cycle characteristics, low temperature characteristics, and output characteristics, it is also equal to or above the previous double-layer capacitor. The specific surface area of graphite is a few hundredths of the specific surface area of activated carbon, and the difference in the decomposition of the electrolyte is caused by the great difference in the specific surface area.

For the new concept capacitor using graphite as the positive electrode active material, the durability is not enough, which hinders its practical application. However, according to the technology of using aluminum coated with amorphous carbon film for collector (refer to patent document 3), it can be known that the high temperature durability can be improved to a practical level. In addition, the capacitor of this new concept is a capacitor that uses the reaction of the insertion and separation of electrolyte ions relative to the interlayer of graphite for the positive electrode. It is not a double-layer capacitor in the strict sense, but in patent document 3, it is broadly referred to as a double-layer capacitor.

In addition, even for the negative electrode, a storage device that uses metal oxides such as lithium titanate and lithium-containing niobium oxide as negative electrode active materials instead of activated carbon and utilizes the reaction of insertion and separation of lithium ions relative to the interlayer of lithium titanate has been proposed (for example, see patent documents 2 and 4). During charging and discharging, the electrolyte anions and lithium cations contained in the electrolyte move toward the positive electrode or the negative electrode in opposite directions, respectively, so it is called a dual-ion battery (DIB). Compared with lithium-ion secondary batteries in which only lithium ions move, DIBs have excellent output characteristics and lifespan, and it is expected that there is no need to set restrictions on SOC (state of charge).

Prior art literature

Patent Document 1: Japanese Patent Application Publication No. 2011-046584

Patent Document 2: Japanese Patent Application Publication No. 2010-040180

Patent Document 3: Japanese Patent No. 6167243

Patent Document 4: Japanese Patent No. 4465492

Summary of the invention

Problems to be solved by the invention

As the above two types of power storage devices, hybrid capacitors and dual-ion batteries can increase energy density by several times compared to conventional double-layer capacitors (EDLCs). On the other hand, regarding the high output characteristics that are a major feature of EDLCs, hybrid capacitors and dual-ion batteries also have high output characteristics like EDLCs. However, there are problems in the intention of further high output.

The present invention is made in view of the above situation. The present invention focuses on the collector of the electrode of the storage device such as the hybrid capacitor and the dual ion battery (the collector for the storage device electrode), and the purpose is to further develop the amorphous carbon film included in the collector for the storage device electrode, thereby providing a storage device that achieves further high output, maintains high energy density and has excellent output characteristics. In addition, the purpose of the present invention is to provide a collector for the electrode of the storage device with excellent output characteristics, and a method for manufacturing the collector for the electrode of the storage device with excellent output characteristics.

Means of solving problems

In order to solve the above-mentioned problems, the present invention provides the following means.

[1] A current collector for an electrode of a power storage device, comprising: an aluminum material; and an amorphous carbon film formed on the aluminum material.

In the amorphous carbon film, the ratio of sp ² bonded carbon to the total amount of sp ² bonded carbon and sp ³ bonded carbon (sp ² /(sp ³ +sp ² )) is 0.35 or more.

The ratio (sp ² /(sp ³ +sp ² )) is a ratio measured by an X-ray absorption fine structure (XAFS) method.

[2] The current collector for a power storage device electrode according to [1], wherein the current collector for a power storage device electrode is a current collector for a positive electrode of a hybrid capacitor or a current collector for a positive electrode of a dual ion battery,

The positive electrode of a hybrid capacitor or a dual-ion battery contains graphite as a positive electrode active material.

[3] The current collector for a power storage device electrode according to [1], wherein the current collector for a power storage device electrode is a current collector for a negative electrode of a hybrid capacitor or a current collector for a negative electrode of a dual ion battery,

The negative electrode of the hybrid capacitor or the negative electrode of the dual ion battery contains one selected from the group consisting of activated carbon, graphite, hard carbon, soft carbon, and lithium titanate as a negative electrode active material.

[4] A method for producing a current collector for an electrode of a power storage device, comprising:

A film forming step of forming an amorphous carbon film on the aluminum material; and

In the heat treatment step, the amorphous carbon film is heat-treated at a temperature of 400° C. or higher.

[5] The method for producing a current collector for a power storage device electrode according to [4], wherein a heat treatment step is performed after the film forming step.

[6] A current collector for an electrode of a power storage device, comprising: an aluminum material; and an amorphous carbon film formed on the aluminum material.

The amorphous carbon film is obtained by the production method described in [4] or [5].

[7] An electric storage device comprising at least a positive electrode, a negative electrode and an electrolyte,

The positive electrode includes a positive electrode active material, and the negative electrode includes a negative electrode active material,

The positive electrode active material includes graphite,

The current collector on the positive electrode side is the current collector for a power storage device electrode as described in any one of [1] or [6],

The thickness of the amorphous carbon film is not less than 60 nm and not more than 300 nm.

[8] The power storage device according to [7], wherein the graphite includes rhombohedral crystals.

[9] The power storage device according to [7] or [8], wherein the negative electrode active material includes one selected from the group consisting of activated carbon, graphite, hard carbon, soft carbon, and lithium titanate,

The current collector on the negative electrode side is one selected from the group consisting of the current collector for the power storage device electrode described in [1] and [7], etched aluminum, and an aluminum material.

According to the present invention, it is possible to provide a power storage device, which can achieve further high output, maintain high energy density and have excellent output characteristics by further developing the amorphous carbon film included in the current collector for the electrode of the power storage device. In addition, according to the present invention, it is possible to provide a current collector for an electrode of a power storage device with excellent output characteristics and a method for manufacturing a current collector for an electrode of a power storage device with excellent output characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a NEXAFS spectrum for explaining the XAFS measurement method.

Detailed ways

The materials, dimensions, and the like described in the following description are merely examples, and the present invention is not limited thereto, and can be implemented with appropriate modifications within the scope of the present invention.

(Current Collector for Electricity Storage Device Electrode)

The collector for an electrode of a power storage device of the present invention comprises an aluminum material and an amorphous carbon film formed on the aluminum material. The amorphous carbon film is characterized in that the ratio of ^sp2 bonded carbon to the total amount of ^sp2 bonded carbon and ^sp3 bonded carbon (referred to as " ^sp2 /( ^sp3 + ^sp2 ) ratio") is 0.35 or more. In addition, the ^sp2 /( ^sp3 + ^sp2 ) ratio is a ratio measured by an X-ray Absorption Fine Structure (XAFS) method. The XAFS method will be described in detail later. In addition, a conductive carbon layer can be formed between the amorphous carbon film and the positive electrode active material, or between the amorphous carbon film and the negative electrode active material.

In order to achieve a particularly good effect, the current collector for the storage device electrode of the present invention is preferably used for a hybrid capacitor positive electrode containing graphite as a positive electrode active material, or as a dual ion battery positive electrode current collector containing graphite as a positive electrode active material. In addition, the current collector for the storage device electrode of the present invention can also be used as a hybrid capacitor negative electrode current collector, or as a dual ion battery negative electrode current collector.

Here, the "hybrid capacitor" of the present invention is an electric storage device that utilizes the double-layer principle of adsorption or desorption of electrolyte cations at the negative electrode and the principle of intercalation-deintercalation of electrolyte anions relative to graphite at the positive electrode. For example, a hybrid capacitor that uses activated carbon for the negative electrode and graphite for the positive electrode can be cited.

Here, the "dual ion battery" of the present invention is an electrical storage device that utilizes the principle of intercalation-deintercalation of lithium ions at the negative electrode and the principle of intercalation-deintercalation of electrolyte anions relative to graphite at the positive electrode. Both "hybrid capacitors" and "dual ion batteries" are electrical storage devices in which electrolyte anions and cations are inserted or adsorbed relative to the positive and negative electrodes during charging, and are decoupled or released during discharging. This is different from the principle that lithium ions move in the positive electrode during charging and discharging, such as lithium ion batteries. More specifically, lithium ions in the positive electrode of a lithium ion battery move to the negative electrode during charging (lithium ion insertion reaction) and discharge (lithium ion desorption reaction).

The current collector for a power storage device electrode of the present invention is preferably obtainable by the production method described below.

＜Aluminum＞

As the aluminum material serving as the substrate, an aluminum material generally used for a current collector can be used.

The aluminum material may be in the form of a foil, a sheet, a film, a mesh, etc. Aluminum foil can be suitably used as a current collector.

In addition, in addition to using flat aluminum as the aluminum material, the aluminum material described later may also be used.

There is no particular limitation on the thickness of the aluminum material when it is a foil, sheet or film. When the size of the battery itself is the same, the thinner the aluminum material, the more active material can be loaded into the battery shell. However, due to the reduced strength, an appropriate thickness should be selected. As an actual thickness, it is preferably 10 μm to 40 μm, and more preferably 15 μm to 30 μm. When the thickness is less than 10 μm, there is a possibility that the aluminum material will break or crack in the process of roughening the surface of the aluminum material or in other manufacturing processes.

As the aluminum material, etched aluminum can be used.

Etched aluminum is an aluminum material that has been roughened by etching. Etching is usually performed by immersing in an acid solution such as hydrochloric acid (chemical etching) or electrolyzing aluminum as an anode in an acid solution such as hydrochloric acid (electrochemical etching). In electrochemical etching, the etching shape varies depending on the current waveform during electrolysis, the composition of the solution, the temperature, etc., so it can be selected based on the performance of the storage device.

The aluminum material may have a passivation layer on the surface or may not have a passivation layer on the surface. When a passivation film as a natural oxide film is formed on the surface of the aluminum material, an amorphous carbon coating layer may be provided on the natural oxide film, or the amorphous carbon coating layer may be provided after the natural oxide film is removed by, for example, argon sputtering.

The natural oxide film on the aluminum material is a passivation film, which itself has the limitation of being difficult to be corroded by the electrolyte. On the other hand, it will increase the resistance of the collector. Therefore, from the viewpoint of reducing the resistance of the collector, it is preferable that there is no natural oxide film.

＜Amorphous carbon film＞

In this specification, the term "amorphous carbon film" refers to an amorphous (amorphous structure) carbon film or a hydrogenated carbon film. Generally, ^sp2 bonded carbon and ^sp3 bonded carbon are contained in a certain ratio. The ratio of sp2 bonded carbon to the total amount of ^sp2 bonded carbon and ^sp3 bonded carbon (also referred to as ^sp2 /( ^sp3 +sp2) ratio) of the amorphous carbon film used for the collector for the electrode of the power storage device of the present invention (hereinafter referred to as "the amorphous carbon ^film of the present invention") is 0.35 or more. In addition, the ( ^sp2 /( ^sp3 + ^sp2 )) ratio is a ratio measured by the X-ray absorption fine structure (XAFS) method. ^{The sp2 /} ( ^sp3 + ^sp2 ) ratio is preferably 0.40 or more.

The sp ² /(sp ³ +sp ² ) ratio is preferably 0.6 or less, more preferably 0.5 or less, from the viewpoints of maintaining high chemical resistance and obtaining higher conductivity and that a higher sp ² ratio makes the layer softer and improves adhesion to the active material layer.

A power storage device using the power storage device electrode collector having an amorphous carbon film of the present invention (hereinafter referred to as "power storage device electrode collector of the present invention") can maintain high energy density and improve output characteristics. In particular, a power storage device using the power storage device electrode collector of the present invention as a collector of a positive electrode composed of a graphite active material is suitable because it can maintain high energy density and further improve output characteristics.

Here, the XAFS method is described.

In general, each element has the property of strongly absorbing X-rays with energy equivalent to the binding energy of the inner-shell electron. Here, the part where the absorption coefficient of X-rays in the material increases significantly is called the absorption edge, and the energy of X-rays equivalent to the absorption edge is called the X-ray absorption edge energy. Each element has a different inner-shell electron binding energy. If an X-ray with an energy greater than the inner-shell electron binding energy is irradiated, the absorption coefficient of X-rays increases with the emission of inner-shell electrons. Therefore, for a certain element, the X-ray absorption spectrum is measured and the absorption edge is observed, thereby obtaining information on the X-ray absorption fine structure (XAFS vibration) that reflects the environment and structure around the element. By analyzing the XAFS vibration, the local structure around the element of interest can be known. In addition, based on the change in the electronic state of the element, it can be known that the position of the absorption edge moves, and by comparing the absorption edge, the valence of the element of interest can be known. The measurement methods for obtaining the average X-ray absorption spectrum in the sample as described above using the XAFS method include the transmission method and the fluorescence yield method. The transmission method is a method in which the X-ray intensity before and after the sample is irradiated with X-rays to directly measure the X-ray absorption. The fluorescence yield method is a method in which the fluorescence X-rays emitted from atoms that absorb and are excited by the X-rays are measured when the sample is irradiated with X-rays. Regardless of which method is used, the same results can be obtained for the local structure and valence of the element to be analyzed.

XAFS is divided into the X-ray near absorption edge fine structure (NEXAFS: Near Edge X-ray Absorption Fine Structure, or XANES: X-ray Absorption Near Edge Structure) that appears in the region of about 50 eV from the absorption edge and the extended X-ray absorption fine structure (EXAFS: Extended X-ray Absorption Fine Structure) that appears at energies above 50 eV. On the other hand, the peak of NEXAFS that appears in the region of about 50 eV from the absorption edge corresponds to the energy of the inner shell electron transition to the empty orbital non-occupied orbital, and a spectral structure that depends on the valence number, coordination structure, etc. of the element of interest is obtained. Thus, the characteristic of NEXAFS is that excitation to the empty orbital can be observed. As described below, the XAFS measurement method of the present invention uses NEXAFS in order to be able to determine the ^sp2 /( ^sp2 + ^sp3 ) ratio of the diamond-like carbon (DLC) film with high accuracy.

FIG. 1 shows a carbon atom K-edge NEXAFS spectrum of a conventional DLC film. The ionization energy of carbon is 295 eV, so it includes photoelectrons generated by direct photoionization with an energy higher than this energy. The portion shown as direct ionization in FIG. 1 includes photoelectrons, normal Auger electrons as its subsequent reaction, and secondary electrons emitted thereby. The broad peak existing between 290 eV and 310 eV reflects the Auger electrons originating from the C1s→σ* resonant Auger electron emission process and the secondary electrons emitted thereby. The peak observed near 285.4 eV reflects the Auger electrons originating from the 1s→π* resonant Auger electron emission process and the secondary electrons emitted thereby. In the NEXAFS measurement method, by avoiding 1s→π* for observation, the sp ² /(sp ² +sp ³ ) ratio can be determined with high accuracy. In practice, the ratio (I _π* /I _all ) of the integral value of the absorption intensity in the specified region (I _all ) to the peak area (I _π* ) of 1s→π* is calculated and compared with I _π* /I _all of HOPG having an sp ² composition of 100%, thereby determining the sp ² /(sp ² +sp ³ ) ratio. Detailed measurement and analysis methods are described in the Examples.

The amorphous carbon film of the present invention having an sp ² /(sp ³ +sp ² ) ratio of 0.35 or more includes, for example, a diamond-like carbon (DLC) film, a carbon hard film, an amorphous carbon (aC) film, a hydrogenated amorphous carbon (aC:H) film, and the like.

Among the materials of the amorphous carbon film, a diamond-like carbon (DLC) film is preferred. Diamond-like carbon is a material having an amorphous structure in which both diamond bonds (sp ³ ) and graphite bonds (sp ² ) are mixed, and has high chemical resistance. The amorphous carbon film of the present invention having an sp ² /(sp ³ +sp ² ) ratio of 0.35 or more as measured by the XAFS method is preferably a DLC film having a developed graphite structure.

Furthermore, in order to improve the conductivity when used as a film of a current collector, boron or nitrogen may be doped.

The thickness of the amorphous carbon film is preferably between 60 nm and 300 nm. If the thickness of the amorphous carbon film is less than 60 nm, it is too thin, the covering effect of the amorphous carbon film becomes small, and the corrosion of the collector in the constant current constant voltage continuous charging test cannot be fully suppressed. In addition, if the thickness of the amorphous carbon film exceeds 300 nm, the amorphous carbon film becomes a resistor, and the resistance between the amorphous carbon film and the active material layer becomes high, so the appropriate thickness is appropriately selected. The thickness of the amorphous carbon film is more preferably between 80 nm and 300 nm, and more preferably between 120 nm and 300 nm.

The current collector of the power storage device according to one embodiment of the present invention has an amorphous carbon film on the surface of an aluminum material, so that the aluminum material can be prevented from contacting with an electrolyte, and corrosion of the current collector caused by the electrolyte can be prevented. In addition, since the amorphous carbon film of the present invention has an ^sp2 /( ^sp3 + ^sp2 ) ratio of 0.35 or more as measured by an X-ray absorption fine structure (XAFS) method, it has a certain conductivity, can maintain a high energy density, and can improve output characteristics.

The amorphous carbon film of the present invention is preferably obtained by the manufacturing method described below. For example, it is preferably an amorphous carbon film obtained by the manufacturing method described below at a heat treatment temperature of 400°C or more, preferably 500°C or more. In addition, from the perspective of mass production of aluminum foil with a DLC film (referred to as "DLC-coated aluminum foil"), when the amorphous carbon film (DLC film) is formed by a roll-to-roll method, there is a problem that wrinkles are easily generated if a heat treatment step of increasing the temperature while forming the film is performed. Therefore, the present inventors have studied intensively and found that, for example, the following manufacturing method is more preferable: after the film forming step is performed at room temperature, the amorphous carbon film (DLC film not subjected to heat treatment) obtained by the film forming step is subjected to heat treatment at 400°C or more, preferably 500°C or more. This is because the sp ² /(sp ³ +sp ² ) ratio of the amorphous carbon film (DLC film subjected to heat treatment) of the present invention obtained by this manufacturing method is 0.35 or more.

＜Conductive carbon layer＞

The collector for the storage device electrode of one embodiment of the present invention preferably has a conductive carbon layer formed between the amorphous carbon film and the positive electrode active material, or between the amorphous carbon film and the negative electrode active material. For example, compared with the activated carbon negative electrode used in the previous storage device, the thickness of the conductive carbon layer is preferably 5 μm or less, and more preferably 3 μm or less because it is subjected to a lower electrode potential for a long time. This is because if the thickness exceeds 5 μm, the energy density becomes smaller when it becomes a battery or electrode. As a material for the conductive carbon layer, the type is not limited as long as it is carbon with high conductivity, but as carbon with high conductivity, it is preferably graphite, and more preferably only graphite.

The particle size of the material of the conductive carbon layer is preferably 1/10 or less of the size of graphite or the like as the active material. This is because if the particle size is within this range, the contact property at the interface between the conductive carbon layer and the active material layer becomes higher, and the interface (contact) resistance can be reduced. Specifically, the particle size of the carbon material of the conductive carbon layer is preferably 1 μm or less, and more preferably 0.5 μm or less.

By providing a conductive carbon layer, even if pinholes exist in the amorphous carbon film, the pinholes can be sealed, thereby preventing the aluminum material from coming into contact with the electrolyte and preventing corrosion of the current collector caused by the electrolyte.

In addition, by having a conductive carbon layer, the contact resistance between the amorphous carbon film covering the collector and the positive electrode active material, or between the amorphous carbon film and the negative electrode active material can be reduced, the discharge rate can be increased, the output characteristics can be improved, and the high-temperature durability can be improved.

In addition, when forming the conductive carbon layer, a binder is added together with the solvent to form a coating, and the coating is applied to the aluminum foil covered with DLC. As the coating method, screen printing, gravure printing, comma coater (registered trademark), spin coating, etc. can be used. As the binder, cellulose, acrylic acid, polyvinyl alcohol, thermoplastic resin, rubber, organic resin can be used. As the thermoplastic resin, polyethylene and polypropylene can be used, as the rubber, SBR (styrene-butadiene rubber) and EPDM can be used, and as the organic resin, phenol resin, polyimide resin, etc. can be used.

The conductive carbon layer preferably has few gaps between particles and low contact resistance. In addition, as a solvent for dissolving the binder used to form the above-mentioned conductive carbon layer, there are two types of aqueous solutions and organic solvents. If the binder used to form the electrode active material layer is a binder that dissolves in an organic solvent, it is preferred to use the binder that dissolves in an aqueous solution for the conductive carbon layer. On the contrary, in the case where the binder used to form the electrode active material layer is an aqueous solution, it is preferred to use the binder that dissolves in an organic solvent for the conductive carbon layer. This is because if the same solvent is used for the electrode active material layer and the conductive carbon layer, the binder of the conductive carbon layer is easily dissolved when the electrode active material layer is coated, and it is easy to become uneven.

(Method for producing current collector for power storage device electrode)

The method for producing a current collector for a storage device electrode of the present invention is characterized by comprising: a film forming step of forming an amorphous carbon film on an aluminum material; and a heat treatment step of heat-treating the amorphous carbon film at a temperature of 400°C or higher. The order of the film forming step and the heat treatment step may be arbitrary. For example, the film forming step and the heat treatment step may be performed simultaneously (sometimes also referred to as a direct film forming method), or the heat treatment step may be performed after the film forming step (sometimes also referred to as a post-heating film forming method). The treatment temperature of the heat treatment step is preferably 300°C or higher, and preferably 600°C or lower, and more preferably 500°C or lower. On the one hand, increasing the heating temperature increases the sp ² /(sp ³ +sp ² ) ratio and reduces the resistance, which is preferred. On the other hand, the melting point of aluminum of the substrate is 660°C. As the melting point approaches, the aluminum material becomes more easily softened, the aluminum material wrinkles, and the substrate loses its flatness, so the temperature at which wrinkles are less likely to occur is set as the upper limit. In addition, when other metals or aluminum alloys are used as the substrate, the upper limit temperature is different, and the upper limit temperature is set to a temperature at which the substrate does not wrinkle or less than the melting point of each metal.

The manufacturing method of performing the film forming step and the heat treatment step simultaneously (direct film forming method) is a method of forming an amorphous carbon film on an aluminum material while heating the aluminum material or the like in the same atmosphere at, for example, 400° C. or higher.

The manufacturing method of performing a heat treatment process after the film forming process (post-heat treatment film forming method) is a method as follows: after forming an amorphous carbon film on an aluminum material, the aluminum material formed with the amorphous carbon film is subjected to a heat treatment at a temperature above 400°C. The atmosphere for the heat treatment can be, for example, an atmosphere in which no raw material gas is supplied, preferably an argon atmosphere. It is a method of heat treating the aluminum material having the amorphous carbon film obtained by the film forming process at a temperature above 400°C in another container different from the film forming process, for example, in an atmosphere of nitrogen, argon, etc. At this time, the processing temperature of the film forming process is preferably less than 200°C, more preferably below 100°C, and further preferably below 50°C. Room temperature is most preferred.

As a method for manufacturing a current collector for a storage device electrode of the present invention, the above-mentioned post-heating treatment film forming method is preferably used from the viewpoint of mass production. This is because, for example, when a current collector for a storage device electrode of the present invention such as a DLC-coated aluminum foil is manufactured by a roll-to-roll method, if the above-mentioned direct film forming method is used, there is a problem that wrinkles are easily generated.

As a method for forming the amorphous carbon film, a well-known method such as a plasma CVD method using hydrocarbon gas, a sputtering evaporation method, an ion plating method, a vacuum arc evaporation method, etc. can be used. Preferably, a plasma CVD method using hydrocarbon gas is used. In addition, it is preferred that the amorphous carbon film has conductivity to the extent that it can function as a current collector.

When the amorphous carbon film is formed by a plasma CVD method using a hydrocarbon-based gas, the thickness of the amorphous carbon film can be controlled by the energy injected into the aluminum material, specifically, the applied voltage, the applied time, and the temperature.

More specifically, in the collector for the storage device electrode of the present invention, if the amorphous carbon film (e.g., DLC-coated aluminum foil) formed at a temperature of 400° C. or higher of the present invention is used, the sp ² /(sp ³ +sp ² ) ratio measured by the XAFS method is 0.35 or higher. An amorphous carbon film (DLC film) with a developed graphite structure can be obtained. In addition, from the viewpoint of mass production of the amorphous carbon film (DLC-coated aluminum foil), when the amorphous carbon film (DLC-coated aluminum foil) is produced by a roll-to-roll method, there is a problem that wrinkles are easily generated once the film forming temperature is increased. On the other hand, when the film is formed at room temperature, there is a problem that the graphite structure is difficult to develop, although the occurrence of wrinkles can be suppressed. The sp ² /(sp ³ +sp ² ) ratio of the amorphous carbon film (DLC-coated aluminum foil) that has not been heat-treated is 0.29 or lower. When applied to electrodes for hybrid capacitors and dual ion batteries, there is a possibility that the interface resistance between the collector and the active material layer becomes high and the output characteristics are reduced. Therefore, the inventors have made intensive studies and found that in the post-heating film forming method, after film formation at room temperature, the amorphous carbon film (DLC-coated aluminum foil) is subjected to a heat treatment at 400°C or higher in an inert atmosphere, so that the ^sp2 /( ^sp3 + ^sp2 ) ratio can be made 0.35 or higher. This is the same or higher ^sp2 /( ^sp3 + ^sp2 ) as in the case of the direct film forming method in which the film is directly formed at 400°C or higher. By using the obtained amorphous carbon film (DLC-coated aluminum foil) as a collector of a positive electrode made of graphite, the output characteristics can be further improved.

Even with regard to foil wrinkles, which are a problem during direct film formation in the roll-to-roll method, the wrinkle problem can be prevented by the post-heating treatment of the present invention. This is because in the roll-to-roll method, in direct film formation, in addition to the influence of the film formation temperature (the atmospheric temperature during film formation), the temperature of the aluminum foil is increased by the energy of the plasma to a temperature higher than the atmospheric temperature. However, in the post-heating film formation method of the present invention, since only the atmospheric temperature is applied to the foil after film formation, the occurrence of wrinkles can be suppressed.

(Electricity storage device)

A power storage device according to one embodiment of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte.

The power storage device of the present invention is preferably a hybrid capacitor or a dual ion battery.

(Hybrid Capacitor)

Hereinafter, a hybrid capacitor as one embodiment of the power storage device of the present invention will be described in detail.

At least one of the current collector on the negative electrode side and the current collector on the positive electrode side of the hybrid capacitor of this embodiment preferably uses the above-mentioned current collector for the storage device electrode of the present invention. When the positive electrode includes graphite, it is preferred that at least the current collector on the positive electrode side uses the above-mentioned current collector for the storage device electrode of the present invention. It is more preferred that both the current collector on the negative electrode side and the current collector on the positive electrode side use the above-mentioned current collector for the storage device electrode of the present invention.

＜Positive electrode＞

The positive electrode used in the hybrid capacitor of the present embodiment includes a current collector (current collector on the positive electrode side) and a positive electrode active material layer formed thereon. The positive electrode active material layer contains a positive electrode active material, a binder, and a conductive material.

A slurry-like positive electrode material mainly including a positive electrode active material, a binder, and a conductive material in an amount as required may be applied to a current collector on the positive electrode side and dried to form a positive electrode active material layer.

[Positive electrode active material]

The positive electrode active material used in the hybrid capacitor of the present embodiment includes graphite. As graphite, artificial graphite or natural graphite can be used. In addition, as natural graphite, flaky natural graphite and earthy natural graphite are known. Natural graphite can be obtained by crushing the mined raw ore and repeatedly performing a process called flotation beneficiation. In addition, artificial graphite can be manufactured, for example, through a graphitization process in which a carbon material is fired at a high temperature. More specifically, for example, by adding a binder such as asphalt to the raw coke to form it, heating it to about 1300°C for a primary firing, then impregnating the primary fired product in an asphalt resin, and then firing it twice at a high temperature of nearly 3000°C, artificial graphite can be obtained. In addition, graphite in which the surface of graphite particles is covered with carbon can also be used.

The crystal structure of graphite is roughly divided into hexagonal crystals of a layer structure composed of ABAB and rhombohedral crystals of a layer structure composed of ABCABC. Depending on the conditions, the crystal structure of graphite becomes a single state or a mixed state of these structures, but graphite of any one crystal structure can be used, and graphite of a crystal structure in a mixed state can also be used. For example, the ratio of rhombohedral crystals of KS-6 (trade name) graphite made by Imerys Graphite & Carbon Japan Ltd. (Imerys Graphite & Carbon Japan Ltd) used in the examples described later is 26%, and the ratio of rhombohedral crystals of mesophase carbon microbeads (MCMB) as artificial graphite made by Osaka Gas Chemical Co., Ltd. is 0%.

The graphite used in other embodiments of the present invention has a different mechanism for presenting the capacitance of the activated carbon used in the previous EDLC. In the case of activated carbon, the electrolyte ions are adsorbed or desorbed relative to the surface of the activated carbon by utilizing the large specific surface area, thereby presenting capacitance. In contrast, in the case of graphite, the anions as electrolyte ions are intercalated and deintercalated relative to the interlayer of the graphite (intercalation-deintercalation), thereby presenting capacitance. Due to such differences, the storage device using graphite in this embodiment is referred to as a double-layer capacitor in the broad sense in Patent Document 3, but it can also be referred to as a hybrid capacitor, which is distinguished from an EDLC using activated carbon having a double electric layer.

[Current Collector on Positive Electrode Side]

The positive electrode current collector used in the hybrid capacitor of this embodiment is preferably an aluminum material having improved corrosion resistance, that is, an aluminum material coated with an amorphous carbon film, and more preferably the current collector for a power storage device electrode of the present invention is used.

Preferably, the current collector on the positive electrode side further has a conductive carbon layer formed between the amorphous carbon film and the positive electrode active material.

＜Negative electrode＞

The negative electrode used in the hybrid capacitor of the present embodiment includes a current collector (current collector on the negative electrode side) and a negative electrode active material layer formed thereon. The negative electrode active material layer contains a negative electrode active material, a binder, and a conductive material.

The negative electrode active material layer can be formed by applying a slurry of the negative electrode material mainly including the negative electrode active material, the binder, and a conductive material in an amount as required onto the current collector on the negative electrode side and drying the slurry.

[Negative electrode active material]

In order to obtain a power storage device with a high withstand voltage, the negative electrode active material used in the hybrid capacitor of the present embodiment is a carbonaceous material that can adsorb or desorb cations as electrolyte ions.

As the negative electrode active material, a material capable of adsorbing or desorbing cations as electrolyte ions can be used, and for example, a carbonaceous material selected from the group consisting of activated carbon, graphite, hard carbon, and soft carbon can be used.

[Current Collector on Negative Electrode Side]

As the collector on the negative electrode side used in the hybrid capacitor of this embodiment, a well-known collector can be used, or a collector selected from the group consisting of an aluminum material having a conductive carbon layer formed between an amorphous carbon film and a negative electrode active material, an aluminum material coated with an amorphous carbon film, etched aluminum, and an aluminum material can be used. Preferably, an aluminum material having a conductive carbon layer formed between an amorphous carbon film and a negative electrode active material, or an aluminum material coated with an amorphous carbon film is used. These aluminum materials are aluminum materials with improved corrosion resistance. When these aluminum materials are used, the collector for the storage device electrode of the present invention can be used, and when the hybrid capacitor is operated at a high voltage, the high temperature durability performance can be improved.

When the hybrid capacitor of this embodiment uses an aluminum material having a conductive carbon layer formed between an amorphous carbon film and a negative electrode active material or an aluminum material covered with an amorphous carbon film, it is preferable to use the above-mentioned collector for a power storage device electrode of the present invention.

＜Adhesive＞

The electrode used in the hybrid capacitor of the present embodiment preferably further includes a binder.

As the binder, for example, fluororesin, rubber, acrylic resin, olefin resin, carboxymethyl cellulose (CMC) resin, natural polymer can be used. As examples of fluororesin, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) can be cited. As examples of rubber, fluororubber, EPDM rubber, styrene butadiene rubber can be cited. As examples of natural polymer, gelatin, chitosan, alginic acid can be cited. For these binders, one can be used alone, or two or more can be used in combination.

＜Conductive materials＞

The conductive material used in the hybrid capacitor of the present embodiment is not particularly limited as long as it is a material that can make the conductivity of the negative electrode active material layer or the positive electrode active material layer good, and well-known conductive materials can be used. For example, carbon black and carbon fiber can be used. As examples of carbon fibers, carbon nanotubes (CNT) and VGCF (registered trademark) can be cited. Carbon nanotubes can be single-layer carbon nanotubes or multi-layer carbon nanotubes. For these conductive materials, one can be used alone or in combination of two or more.

＜Electrolyte＞

As the electrolyte used in the hybrid capacitor of this embodiment, for example, an organic electrolyte using an organic solvent can be used. As long as it contains electrolyte ions, it is not limited to organic electrolytes. In addition, for example, it can also be a gel. The electrolyte contains electrolyte ions that can be adsorbed and desorbed relative to the electrode. The electrolyte ions are preferably electrolyte ions whose ion diameter is as small as possible. Specifically, ammonium salts, phosphonium salts, or ionic liquids, lithium salts, etc. can be used.

As the ammonium salt, a tetraethylammonium (TEA) salt, a triethylammonium (TEMA) salt, etc. can be used. In addition, as the phosphonium salt, a spiro compound having two five-membered rings, etc. can be used.

As the ionic liquid, any type is acceptable, but from the viewpoint of making it easy to move the electrolyte ions, it is preferably a material with as low a viscosity as possible and high conductivity (conductivity). As cations constituting the ionic liquid, for example, imidazolium ions, pyridinium ions, etc. can be cited. As imidazolium ions, for example, 1-ethyl-3-methylimidazolium (1-ethyl-3-methylimidazolium) (EMIm) ions, 1-methyl-1-propylpyrrolidinium (1-methyl-1-propylpyrrolidinium) (MPPy) ions, 1-methyl-1-propylpiperidinium (1-methyl-1-propylpiperidinium) (MPPi) ions, etc. can be cited. In addition, as lithium salts, lithium tetrafluoroborate LiBF ₄ , lithium hexafluorophosphate LiPF ₆ , etc. can be used.

Examples of the pyridinium ion include 1-ethylpyridinium ion and 1-butylpyridinium ion.

Examples of anions constituting the ionic liquid include BF ₄ ion, PF ₆ ion, [(CF ₃ SO ₂ ) ₂ N] ion, FSI (bis(fluorosulfonyl)imide) ion, and TFSI (bis(trifluoromethylsulfonyl)imide) ion.

As the solvent, acetonitrile, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfone, ethyl isopropyl sulfone, ethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, cyclopentane, N,N-dimethylformamide, dimethyl sulfoxide, etc. can be used. These solvents can be used alone or in combination of two or more.

＜Partition＞

As the separator used in the hybrid capacitor of this embodiment, for reasons such as preventing short circuits between the positive and negative electrodes and ensuring electrolyte retention, cellulose-based paper separators, glass fiber separators, and microporous films of polyethylene and polypropylene are suitable.

As described above, the hybrid capacitor of this embodiment uses the aluminum material coated with the amorphous carbon film of the present invention (the collector for the storage device electrode of the present invention) as the collector on the positive electrode side containing graphite. As a result, the hybrid capacitor of this embodiment can achieve high output, maintain high energy density, and improve output characteristics.

In addition, the hybrid capacitor of another embodiment of the hybrid capacitor of the present embodiment uses the aluminum material coated with the amorphous carbon film of the present invention (the collector for the electrode of the storage device of the present invention) as the collector on the negative electrode side. As a result, the hybrid capacitor of another embodiment of the hybrid capacitor of the present embodiment can further achieve high output, maintain high energy density, and further improve output characteristics.

The aluminum material coated with an amorphous carbon film of the present invention (the current collector for the electrode of the power storage device of the present invention) is preferably used as a current collector for the electrode of a hybrid capacitor having a positive electrode containing graphite. In addition, the aluminum material coated with an amorphous carbon film of the present invention (the current collector for the electrode of the power storage device of the present invention) can also be used as a current collector for the electrode of a power storage device such as EDLC.

(Dual Ion Battery)

A dual ion battery (DIB) as another embodiment of the power storage device of the present invention comprises: a positive electrode including a current collector on the positive electrode side and a positive electrode active material layer formed thereon; and a negative electrode including a current collector on the negative electrode side and a negative electrode active material layer formed thereon. The positive electrode active material comprises graphite, and the negative electrode active material comprises a metal oxide capable of absorbing or releasing cations. The current collector on the positive electrode side and the current collector on the negative electrode side are composed of an aluminum material coated with an amorphous carbon film.

Hereinafter, as another embodiment of the power storage device of the present invention, a dual ion battery will be described in detail, and description of the configuration common to the hybrid capacitor described above will be omitted.

In the present embodiment, the negative electrode is changed from the activated carbon negative electrode of the conventional power storage device to a lithium-containing metal oxide or a lithium-free metal oxide (hereinafter simply referred to as "MO _X ") of the dual ion battery of the present embodiment, so that the charge and discharge capacity of the negative electrode is increased. As a metal oxide containing lithium, for example, lithium titanate can be cited. The problem that the activated carbon of the negative electrode in the conventional power storage device becomes the rate limit and hinders the improvement of energy density is solved. By making the capacity of the graphite of the positive electrode more available, the energy density can be theoretically improved, but this time the problem of reduced cycle life characteristics arises. The reason for this problem is that if MO _X such as lithium titanate is used for the negative electrode, the potential curve of MO _X such as lithium titanate is flat compared to the case where the electrode potential is reduced linearly in an inclined manner when activated carbon is used. Therefore, the potential curve when MO _X such as lithium titanate is used for the negative electrode is compared with the potential curve of activated carbon, and the time of withstanding a lower potential becomes longer. As a result, the collector on the negative electrode side of the dual ion battery of the present embodiment becomes easier to dissolve than the collector on the negative electrode side of the conventional power storage device. As a result, high temperature durability is reduced and charge-discharge cycle life characteristics are reduced. In response to this problem, the inventors have found that by using the collector with improved corrosion resistance of the present embodiment as the collector on the negative electrode side, the dissolution of the collector can be suppressed. That is, by using a negative electrode active material with a larger charge-discharge capacity than activated carbon, the energy density of the battery can be increased, but it causes the effect of dissolution of the collector on the negative electrode side. This problem can be solved by applying the collector with improved corrosion resistance of the present embodiment.

Preferably, at least one of the current collector on the negative electrode side and the current collector on the positive electrode side of the dual ion battery of this embodiment uses the above-mentioned current collector for the storage device electrode of the present invention. When the positive electrode contains graphite, it is preferred that at least the current collector on the positive electrode side uses the above-mentioned current collector for the storage device electrode of the present invention. More preferably, the current collector on the negative electrode side and the current collector on the positive electrode side both use the above-mentioned current collector for the storage device electrode of the present invention.

＜Negative electrode＞

The negative electrode used in the dual ion battery of the present embodiment includes a current collector (current collector on the negative electrode side) and a negative electrode active material layer formed thereon. The negative electrode active material layer contains a negative electrode active material, a binder, and a conductive material.

The negative electrode active material layer can be formed by applying a slurry of the negative electrode material mainly including the negative electrode active material, the binder, and a conductive material in an amount as required onto the current collector on the negative electrode side and drying the slurry.

[Negative electrode active material]

The negative electrode active material of the dual ion battery of this embodiment includes a metal oxide that can absorb or release electrolyte ions, i.e., cations, contained in the electrolyte solution described later. In other words, any material that can reversibly insert and remove cations can be used. As cations, for example, alkali metal ions such as Li, Na, and K, alkaline earth metal ions such as Mg and Ca, etc. can be used.

Here, an example using lithium is illustrated. For example, a metal oxide capable of inserting and deintercalating lithium can be used. More specifically, a metal oxide containing lithium or a metal oxide not containing lithium can be used. As the metal of the metal oxide capable of inserting and deintercalating lithium, groups 4, 5, and 6 of periods 4, 5, and 6 of the periodic table can be used. Specifically, transition metals such as titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum (Mo) are preferably used. As the metal oxide containing lithium, for example, a lithium-containing titanium oxide, i.e., Li ₄ Ti ₅ O ₁₂ , a lithium-containing niobium oxide, i.e., LiNbO ₂ , a lithium-containing vanadium oxide, i.e., Li _1.1 V _0.9 O ₂ , etc. can be used. In addition, as the metal oxide not containing lithium, for example, TiO ₂ , NbO ₂ , V ₂ O ₅ , etc. can be used.

From the viewpoint of further improving high temperature durability, the capacity per unit weight of the negative electrode active material is preferably higher than the capacity per unit weight of the positive electrode active material (graphite) described later. The theoretical capacity of graphite used for the positive electrode is 372mAh/g. However, from the viewpoint of cycle life and the degree of expansion of the graphite positive electrode, the capacity of the graphite positive electrode of the present invention in which anions larger than lithium ions are inserted and detached is preferably 50mAh/g to 100mAh/g. On the other hand, the theoretical capacities of the active materials used for the negative electrode are as follows. Li ₄ Ti ₅ O ₁₂ is 175mAh/g, LiNbO ₂ is 203mAh/g, Li _1.1 V _0.9 O ₂ is 313mAh/g, TiO ₂ is 335mAh/g, NbO ₂ is 214mAh/g, and V ₂ O ₅ is 147mAh/g. The negative electrode using these negative electrode active materials is different from the above-mentioned graphite positive electrode and can be charged and discharged to near the theoretical capacity. Therefore, the practical capacity of the above-mentioned negative electrode active material is greater than the practical capacity (50 mAh/g to 100 mAh/g) of the above-mentioned graphite positive electrode. That is, preferably, the positive electrode active material of the present invention is graphite with a practical capacity of 50 mAh/g to 100 mAh/g, and the negative electrode active material of the present invention is higher than the practical capacity of the graphite positive electrode. More preferably, the positive electrode active material of the present invention is graphite with a practical capacity of 50 mAh/g to 100 mAh/g. More preferably, the negative electrode active material of the present invention is at least one selected from the group consisting of Li ₄ Ti ₅ O ₁₂ , LiNbO ₂ , Li _1.1 V _0.9 O ₂ , TiO ₂ , NbO ₂ and V ₂ O _5. It is further preferred that the positive electrode active material of the present invention is graphite with a practical capacity of 50 mAh/g to 100 mAh/g, and the negative electrode active material of the present invention is Li ₄ Ti ₅ O ₁₂ .

[Current Collector on Negative Electrode Side]

The current collector on the negative electrode side used in the dual ion battery of this embodiment is preferably an aluminum material coated with an amorphous carbon film. The aluminum material coated with an amorphous carbon film is an aluminum material with improved corrosion resistance. In addition, the current collector on the negative electrode side used in the dual ion battery of this embodiment is more preferably a current collector for an electrode of a power storage device using the present invention.

Preferably, the current collector on the negative electrode side further has a conductive carbon layer formed between the amorphous carbon film and the negative electrode active material.

＜Positive electrode＞

The positive electrode used in the dual ion battery of the present embodiment includes a current collector (current collector on the positive electrode side) and a positive electrode active material layer formed thereon. The positive electrode active material layer contains a positive electrode active material, a binder, and a conductive material.

The positive electrode active material layer can be formed by applying a slurry of the positive electrode material mainly including the positive electrode active material, the binder and a conductive material in an appropriate amount onto the current collector on the positive electrode side and drying the slurry.

[Positive electrode active material]

In order to obtain a dual ion battery with a high withstand voltage, the positive electrode active material used in the dual ion battery of the present embodiment contains graphite, which is a carbonaceous material capable of inserting and deintercalating anions as electrolyte ions.

The details of graphite are the same as those described in the above-mentioned section "Positive Electrode Active Material of the Hybrid Capacitor as the Electric Storage Device in One Embodiment of the Present Invention".

[Current Collector on Positive Electrode Side]

Similar to the above-mentioned current collector on the negative electrode side, the current collector on the positive electrode side used in the dual ion battery of this embodiment is preferably an aluminum material coated with an amorphous carbon film. The aluminum material coated with an amorphous carbon film is an aluminum material with improved corrosion resistance. In addition, the current collector on the positive electrode side used in the dual ion battery of this embodiment is more preferably a current collector for an electrode of a power storage device using the present invention.

As with the above-mentioned current collector on the negative electrode side, it is preferred that a conductive carbon film is further formed between the amorphous carbon film and the positive electrode active material.

＜Adhesive＞

Preferably, the negative electrode or positive electrode used in the dual ion battery of the present embodiment further contains a binder.

The binder may be the same type as that used in the power storage device (hybrid capacitor) according to one embodiment of the present invention described above.

＜Conductive materials＞

The conductive material used in the dual ion battery of this embodiment is not particularly limited as long as it is a material that makes the conductivity of the negative electrode active material layer or the positive electrode active material layer good, and well-known conductive materials can be used. For example, the same type of conductive material as that of the power storage device (hybrid capacitor) of one embodiment of the present invention described above can be used.

＜Electrolyte＞

As the electrolyte used in the dual ion battery of this embodiment, for example, an organic electrolyte obtained by dissolving an electrolyte in an organic solvent can be used. The electrolyte contains electrolyte ions that can be inserted into and separated from the electrodes. Specifically, lithium salts and the like can be used.

As the organic solvent, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and propylene trifluorocarbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, etc. can be cited. For these organic solvents, one can be used alone, or two or more can be mixed and used.

Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LIAsF ₆ , and LiN(CF ₃ SO ₂ ) ₂ .

Furthermore, additives may be used in the electrolyte to improve high-temperature durability, charge-discharge cycle characteristics, input-output characteristics, and the like.

＜Partition＞

As the separator used in the dual ion battery of the present embodiment, the same type of separator as that of the power storage device (hybrid capacitor) according to one embodiment of the present invention described above can be used.

[Example]

(Manufacturing Example 1) Manufacture of Current Collector

Preparation of a current collector consisting of aluminum foil coated with DLC

Aluminum foil covered with DLC (sometimes referred to as "DLC-coated aluminum foil" or "DLC-coated Al foil") is a collector on the positive electrode side and a collector on the negative electrode side, which is equivalent to an aluminum material coated with an amorphous carbon film. The manufacturing method of DLC-coated aluminum foil is as described below. For aluminum foil with a purity of 99.99% (made by UACJ Foil Co., Ltd., with a thickness of 20μm), the natural oxide film on the surface of the aluminum foil is removed by argon sputtering. Thereafter, a discharge plasma is generated in a mixed gas of methane, acetylene and nitrogen near the surface of the aluminum foil, and a negative bias voltage is applied to the aluminum material, thereby generating a DLC film.

The atmosphere temperature during film formation was set to 25°C, and the formed DLC-coated aluminum foil was transferred to an argon atmosphere furnace and heated to 500°C as a heat treatment temperature under an argon gas flow (500 mL/min). After that, the temperature was maintained for 1 hour, and then naturally cooled to room temperature to produce a DLC-coated aluminum foil (A). Here, when the thickness of the DLC film on the aluminum foil coated with DLC was measured using a probe-type surface shape measuring instrument DektakXT manufactured by BRUKER, the thickness was 150 nm. The result of measuring the DLC-coated aluminum foil (A) by the XAFS method described later showed that the sp ² /(sp ³ +sp ² ) ratio was 0.43. The results are shown in Table 1.

＜Evaluation method: XAFS method＞

NEXAFS analysis was performed using the BL-2 ultrasoft X-ray spectroscopy line at the Ritsumeikan University SR Center, and the spectrum was obtained by the total electron yield method (TEY: Total Electron Yield) based on sample current measurement. The measured NEXAFS spectrum is the C K edge (260 to 345 eV). The slit size is 25μm×25μm, the incident angle of the X-ray to the sample is 90°, and the spectrum integration time is set to 30 minutes each.

The energy axis calibration was performed based on the literature value of highly oriented pyrolytic graphite (HOPG) as a standard sample. In addition, the sp ² /(sp ³ +sp ² ) ratio was calculated using the spectrum of HOPG measured on the same day as a reference.

(Production Examples 2 to 5)

DLC-coated aluminum foil (B), DLC-coated aluminum foil (C), DLC-coated aluminum foil (D), and DLC-coated aluminum foil (E) were produced by the same post-heat treatment method as in Production Example 1, except that the heat treatment temperatures were 100°C, 200°C, 300°C, and 400°C, respectively. The sp ² /(sp ³ +sp ² ) ratio of the obtained DLC-coated aluminum foil was measured by the same method as in Production Example 1. The results are shown in Table 1.

(Production Example 6)

A DLC-coated aluminum foil (F) was produced in the same manner as in Production Example 1, except that the DLC-coated aluminum foil formed at an atmospheric temperature of 25°C was not subjected to heat treatment and was naturally cooled to room temperature. The sp ² /(sp ³ +sp ² ) ratio of the obtained DLC-coated aluminum foil was measured in the same manner as in Production Example 1. The results are shown in Table 1.

[Table 1]

(Synthesis Example 1) Synthesis of Negative Electrode Active Material

Synthesis of Lithium Titanate

Anatase-type titanium oxide with an average particle size of 3 μm and lithium hydroxide were weighed so that the stoichiometric ratio of titanium to lithium was 5:4 moles, placed in a crucible, and placed in an electric atmosphere furnace, and calcined at 800° C. for 5 hours in the atmosphere to obtain lithium titanate (Li ₄ Ti ₅ O ₁₂ , LTO).

"Fabrication of Hybrid Capacitors"

(Example 1)

(1) Preparation of slurry for storage device electrodes

As positive electrode active materials, graphite of Yiruishi and graphite made by Carbon Japan Co., Ltd. (trade name: KS-6, average particle size 6 μm), acetylene black (conductive material) and polyvinylidene fluoride (organic solvent binder) were weighed so that the weight percentage concentration (wt%) ratio was 80:10:10. They were dissolved and mixed in N-methylpyrrolidone (organic solvent) to prepare the positive electrode slurry of this embodiment.

As negative electrode active materials, activated carbon YP-50F manufactured by Kuraray Co., Ltd., acetylene black (conductive material), carboxymethyl cellulose (aqueous solution type binder 1) and polyacrylic acid (aqueous solution type binder 2) were weighed in a ratio of 85wt%:5wt%:5wt%:5wt%. Thereafter, they were dissolved and mixed in pure water to prepare the negative electrode slurry of this example.

(2) Fabrication of electrodes for power storage devices

The DLC-coated aluminum foil (A) obtained in the manufacturing example 1 is used as the collector on the positive electrode side. The prepared positive electrode slurry is applied to the collector on the positive electrode side using a table coater, and then dried at 100°C for 1 hour to produce the positive electrode of this example.

When the thickness of the positive electrode was measured using a micrometer, the thickness was 68 μm.

An etched aluminum foil (thickness 20 μm) manufactured by Nippon Electric Storage Industry Co., Ltd. was used as the collector on the negative electrode side. The prepared negative electrode slurry was applied to the collector on the negative electrode side using a desktop coater and then dried at 100°C for 1 hour to produce the negative electrode of this embodiment.

When the thickness of the negative electrode was measured using a micrometer, it was 88 μm.

＜Preparation of button cell type hybrid capacitor＞

Next, the obtained positive electrode was punched into a disc with a diameter of 16 mm, and the obtained negative electrode was punched into a disc with a diameter of 14 mm, and the parts were vacuum dried at 150°C for 24 hours. Thereafter, it was moved to an argon glove box. The dried positive electrode and negative electrode were stacked with a paper separator (trade name: TF4540) made by Nippon Kodo Paper Industry Co., Ltd. Add 0.1 mL of an electrolyte solution using 1M SBP- _BF4 (5-nitrogenium spiro [4.4] nonane tetrafluoroborate) as an electrolyte and PC (propylene carbonate) as a solvent, and a 2032-type button battery as a hybrid capacitor of this embodiment was made in an argon glove box.

The obtained hybrid capacitor was evaluated for discharge rate characteristics and discharge capacity improvement rate by the evaluation method described below. The results are shown in Table 2.

(Example 2)

The positive electrode of Example 2 was prepared by the same method as in Example 1 except that the DLC-coated aluminum foil (E) obtained in the manufacturing example 5 was used. In addition, a hybrid capacitor was prepared by the same method as in Example 1 except that the positive electrode of Example 2 was used. The discharge rate characteristics and the discharge capacity improvement rate of the obtained hybrid capacitor were evaluated by the evaluation method described later. The results are shown in Table 2.

(Comparative Example 1)

The positive electrode of Comparative Example 1 was prepared by the same method as in Example 1 except that the DLC-coated aluminum foil (F) obtained in Manufacturing Example 6 was used. In addition, a hybrid capacitor was prepared by the same method as in Example 1 except that this positive electrode was used. The discharge rate characteristics and discharge capacity improvement rate of the obtained hybrid capacitor were evaluated by the evaluation method described later. The results are shown in Table 2.

(Comparative Examples 2 to 4)

The positive electrodes of Comparative Examples 2 to 4 were prepared by the same method as in Example 1 except that the DLC-coated aluminum foil (B), DLC-coated aluminum foil (C), and DLC-coated aluminum foil (D) obtained in the above-mentioned Manufacturing Examples 2 to 4 were used respectively. In addition, a hybrid capacitor was prepared by the same method as in Example 1 except that the positive electrode was used. The discharge rate characteristics and the discharge capacity improvement rate of the obtained hybrid capacitor were evaluated by the evaluation method described later. The results are shown in Table 2.

[Table 2]

*1 is a value normalized with Comparative Example 1 being 100.

※2Discharge rate characteristics: Capacity at 14mA/ ^cm2 /Capacity at 0.2mA/ ^cm2

"Preparation of dual-ion batteries"

＜Production of negative electrode＞

As the negative electrode active material, lithium titanate (Li ₄ Ti ₅ O ₁₂ , LTO), acetylene black (conductive material), and polyvinylidene fluoride (organic solvent-based binder) obtained by synthesis 1 were weighed so that the weight percentage concentration (wt%) ratio was 80:10:10. The negative electrode slurry obtained by dissolving and mixing them with N-methylpyrrolidone (organic solvent) was applied to flat aluminum (プレーンAl) (made of foil manufactured by UACJ Co., Ltd., thickness 20μm) using a scraper. Thereafter, drying was performed to obtain the negative electrode of this example. When the thickness of the negative electrode was measured using a micrometer, its thickness was 48μm.

＜Production of button cell type dual ion battery＞

A 2032-type button cell as a dual-ion battery of this embodiment was prepared by the same method as in Example 1, except that the prepared negative electrode of this embodiment was used and 3-LiPF ₆ /EMC was used as the electrolyte. The discharge rate characteristics and discharge capacity improvement rate of the obtained dual-ion battery were evaluated by the evaluation method described below. The results are shown in Table 3.

(Example 4)

A button cell was produced by the same method as in Example 3 except that the DLC-coated aluminum foil (A) obtained in Manufacturing Example 1 was used as the current collector on the negative electrode side. The discharge rate characteristics and discharge capacity improvement rate of the obtained dual ion battery were evaluated by the evaluation method described below. The results are shown in Table 3.

(Comparative Example 5)

A button cell was produced by the same method as in Example 3 except that the same positive electrode as in Comparative Example 1 was used. The discharge rate characteristics and discharge capacity improvement rate of the obtained dual ion battery were evaluated by the evaluation method described below. The results are shown in Table 3.

[table 3]

*1 is a value normalized with Comparative Example 5 being 100.

※2Discharge rate characteristics: Capacity at 14mA/ ^cm2 /Capacity at 0.2mA/ ^cm2

(Test 1) Evaluation of power storage device

＜Discharge rate characteristics＞

For the obtained battery, a charge and discharge test device BTS2004 manufactured by Nagano Co., Ltd. was used to perform constant current and constant voltage charging at a current density of 0.2mA/ ^cm2 or 14mA/ ^cm2 and a voltage of 3.5V in a constant temperature chamber at 25°C. Thereafter, the charge and discharge test was performed by discharging at a discharge current value of a current density of 0.2mA/ ^cm2 until a specified termination voltage was reached. Here, the test was performed with a discharge termination voltage of 0V in the case of the hybrid capacitors of Examples 1 to 4 and Comparative Examples 1 to 4, and a discharge termination voltage of 2V in the case of the dual ion battery of Examples 5, 6 and Comparative Example 5. The ratio of the discharge capacity at 14mA/ ^cm2 to the discharge capacity in the case of a charge and discharge test at a current density of 0.2mA/ ^cm2 obtained as a test result was calculated to obtain the discharge rate. The results are shown in Tables 2 and 3. In Table 2, the results of the discharge rate characteristics of Examples 1 and 2 and Comparative Examples 2 and 3 show values standardized with the value of the discharge rate of Comparative Example 1 as 100. For example, when the discharge rate of Comparative Example 1 is X and the discharge rate of Example 1 is Y, the discharge rate characteristics of Comparative Example 1 are 100, and the discharge rate characteristics of Example 1 are 100Y/X. In Table 3, the results of the discharge rate characteristics of Examples 3 and 4 show values standardized with Comparative Example 5 as 100.

(Test 2) Evaluation of power storage device

＜Discharge capacity improvement rate＞

For the obtained battery, a charge and discharge test device BTS2004 manufactured by Nagano Co., Ltd. was used to perform constant current and constant voltage charging at a current density of 0.2 mA/ ^cm2 and a voltage of 3.5 V in a constant temperature chamber at 25°C. Thereafter, the charge and discharge test was performed by discharging at a discharge current value of a current density of 0.2 mA/ ^cm2 until a specified termination voltage. In addition, the discharge capacity before the constant current and constant voltage continuous charging test was measured. Here, the test was performed with the termination voltage of the discharge in the case of the hybrid capacitor being 0V and the termination voltage of the discharge in the case of the dual ion battery being 2V.

Next, a continuous charging test (constant current and constant voltage continuous charging test) was performed in a 60°C thermostat using a charge and discharge test device BTS2004 at a current density of 0.2mA/ ^cm2 and a voltage of 3.5V. Specifically, charging was stopped within a specified time during charging, and the battery was moved to a 25°C thermostat, and then constant current and constant voltage charging was performed in the same manner as above at a current density of 0.2mA/ ^cm2 and a voltage of 3.5V. Thereafter, the battery was discharged at a discharge current value of a current density of 0.2mA/ ^cm2 until a specified termination voltage was reached. The discharge capacity was obtained by performing this charge and discharge test 5 times. Here, the test was performed with a discharge termination voltage of 0V in the case of a hybrid capacitor and a discharge termination voltage of 2V in the case of a dual ion battery. Thereafter, the battery was returned to the 60°C thermostat and the continuous charging test was restarted. The test was performed until the total continuous charging test time was 2000 hours. The discharge capacity at this time was measured.

The discharge capacity improvement rate is a value normalized by setting the discharge capacity maintenance rate after the constant-current constant-voltage continuous charging test to a charging time at which the discharge capacity before the constant-current constant-voltage continuous charging test becomes 80% or less and the life of the comparative example as a comparison object as 100.

In Table 2, the results of the discharge capacity improvement rates of Examples 1 and 2 and Comparative Examples 2 and 3 show the values normalized by setting the value of the discharge capacity improvement rate of Comparative Example 1 to 100. In Table 3, the results of the discharge capacity improvement rates of Examples 3 and 4 show the values normalized by setting the discharge capacity improvement rate of Comparative Example 5 to 100.

As shown in Table 2, Examples 1 and 2 using the current collector for storage device electrodes of the present invention obtained excellent discharge rate characteristics and discharge capacity improvement rates compared with Comparative Examples 1 to 4. Similarly, as shown in Table 3, Examples 3 and 4 using the current collector for storage device electrodes of the present invention obtained excellent discharge rate characteristics and discharge capacity improvement rates compared with Comparative Example 5. The sp 2 /(sp 3 +sp 2 ) ratio measured by the XAFS method of the DLC-coated aluminum foil (A), DLC-coated aluminum foil (E), DLC-coated aluminum foil (F), and DLC-coated aluminum foil ( ^G ) formed at a temperature of 400 ^° C or above was ^0.35 or more. Therefore, it is a DLC film with a developed graphite structure. When the current collector for storage device electrodes including the DLC film is applied to the positive electrode for the hybrid capacitor of Examples 1 to 4 and the dual ion battery of Examples 5 and 6, it is believed that the interface resistance between the collector and the active material layer can be reduced, and the output characteristics can be improved.

It was found that the power storage device of Example 1 exhibited superior characteristics compared with the power storage device of Example 2 because the sp ² /(sp ³ +sp ² ) ratio of the DLC-coated aluminum foil (A) obtained at a treatment temperature of 500° C. or higher was 0.40 or higher.

In Example 4, both the collector on the negative electrode side and the collector on the positive electrode side use the collector for storage device electrodes of the present invention (covered with DLC aluminum foil (A). In Example 3, only the collector on the positive electrode side uses the collector for storage device electrodes of the present invention (covered with DLC aluminum foil (A). Compared with Example 3, Example 4 has the same discharge rate characteristics, but further improves the discharge capacity improvement rate. It is found that the collector for storage device electrodes of the present invention is effective even when applied to the negative electrode.

Claims (9)

1. A collector for an electrode of a power storage device, comprising an aluminum material and an amorphous carbon film formed on the aluminum material, characterized in that: In the amorphous carbon film, a ratio of sp ² bonded carbon to a total amount of sp ² bonded carbon and sp ³ bonded carbon (sp ² /(sp ³ +sp ² )) is 0.35 or more and 0.5 or less, The ratio (sp ² /(sp ³ +sp ² )) is a ratio measured by the X-ray absorption fine structure (XAFS) method. The current collector for a power storage device electrode is formed by a manufacturing method including a film forming step of forming an amorphous carbon film on an aluminum material and a heat treatment step of heating the amorphous carbon film at a temperature of 400° C. or higher after the film forming step. 2. The current collector for an electrode of a power storage device according to claim 1, wherein the current collector for an electrode of a power storage device is a positive electrode current collector for a hybrid capacitor or a positive electrode current collector for a dual ion battery, wherein: The hybrid capacitor positive electrode or the dual ion battery positive electrode contains graphite as a positive electrode active material. 3. The current collector for an electrode of a power storage device according to claim 1, wherein the current collector for an electrode of a power storage device is a current collector for a negative electrode of a hybrid capacitor or a current collector for a negative electrode of a dual ion battery, wherein: The hybrid capacitor negative electrode or the dual ion battery negative electrode includes one selected from the group consisting of activated carbon, graphite, hard carbon, soft carbon, and lithium titanate as a negative electrode active material. 4. A method for manufacturing a current collector for an electrode of a power storage device according to claim 1, characterized in that it comprises: A film forming step of forming an amorphous carbon film on the aluminum material; and The heat treatment step heats the amorphous carbon film at a temperature of 400° C. or higher. 5 . The method for producing a current collector for a power storage device electrode according to claim 4 , wherein the heat treatment step is performed after the film forming step. 6. A collector for an electrode of a power storage device, comprising an aluminum material and an amorphous carbon film formed on the aluminum material, characterized in that: The amorphous carbon film is obtained by the production method according to claim 4 or 5. 7. A power storage device, which is composed of at least a positive electrode, a negative electrode and an electrolyte, characterized in that: The positive electrode includes a positive electrode active material, and the negative electrode includes a negative electrode active material, The positive electrode active material comprises graphite, The current collector on the positive electrode side is the current collector for an electrode of a power storage device according to claim 1 or 6. The power storage device according to claim 7 , wherein the graphite includes rhombohedral crystals. 9. The power storage device according to claim 7 or 8, wherein: The negative electrode active material includes one selected from the group consisting of activated carbon, graphite, hard carbon, soft carbon and lithium titanate, The current collector on the negative electrode side is one selected from the group consisting of the current collector for the power storage device electrode according to claims 1 and 6, etched aluminum, and an aluminum material.